Event Reduction in Localization of DES Supervisory Control

Supervisor localization procedure has been employed to construct local controllers corresponding to component agents in discrete-event systems. The proposed method in [11] is based on state reduction of a monolithic supervisor with respect to each set of controllable events corresponding to each component agent. A supervisor is localizable if state cardinality in each local controller is less than the number of states in the reduced supervisor, constructed by the proposed method in [10]. A supervisor is reducible if state cardinality of the constructed generator by the supervisor reduction procedure is less than the number of states of the original supervisor. In this paper, we define exclusive control consistency (ECC) property for a pair of states and prove that this property is a sufficient condition to guarantee reducing the event cardinality in each local controller comparing to the reduced supervisor. It is shown that reducibility and localizability properties are stronger than having ECC states in the original supervisor. The implementation of local controllers on industrial systems is facilitated by state reduction, whereas communication traffic between each pair of local controllers is reduced by event reduction.